Recently, wireless services are introduced to advance a ubiquitous society where all materials and objects are sophisticated and exchange information by being connected in an electronic space.
The ubiquitous can be successful only through a wireless network. Accordingly, current wireless communication base has been diversely developed. A Wireless Personal Area Network (WPAN), which is one of wireless communication bases, includes a bluetooth, ultra wideband (UWB), zigbee, and WiMedia.
In particular, the WiMedia as a compound word of wireless and a media is a wireless technology for removing a connection cable in a home networking. The WiMedia enables super-high speed data transfer between electronic home appliances such as a computer, Personal Digital Assistant (PDA), an MP3 player, a digital television (TV), a high definition TV (HDTV), a Digital Versatile Disc (DVD) player, a digital camcorder, a digital set-top box, and a game console.
WiMedia Medium Access Control (MAC) includes a Distributed Reservation Protocol (DRP) and Priority Contention Access (PCA). The DRP is a protocol similar to Time Division Multiplexing Access (TDMA) and denotes a method for reserving a data propagation time in advance and transferring data at the reserved time. The PCA is a method for transferring data based on different backoffs according to 4 priorities.
A conventional WiMedia MAC operation will be described hereinafter. FIG. 1 shows the conventional WiMedia MAC operation.
Referring to FIG. 1, a superframe 101 includes 256 Medium Access Slots (MASs) 121. The superframe 101 is divided into a beacon period 110 and a data transfer period 120.
In the data transfer period 120, the data are transferred according to a DRP 122 and a PCA 123. The beacon period 110 includes beacon slots and only beacons in the beacon slot are transferred. The beacon synchronizes a network.
The DRP 122 includes a method for reserving a transfer period in the beacon period 110 and transferring data in the reserved transfer period, which is called an Implicit Negotiation (IN) method, and a method for reserving the MAS 121 through DRP negotiation and transferring data in the reserved transfer period, which is called an Explicit Negotiation (EN) method.
The IN method reserves own data transfer period 120 by loading a DRP information element (IE) in a beacon in the beacon period 110. The EN method reserves own data transfer period 120 of the DRPs 122 by transferring a reserve request frame to the PCA 123 before the DRP 122. The IN method and the EN method initialize the DRP information element in a transfer station and include the number of the MASs 121 in the superframe 100.
When two stations reserve the same MAS 121, a collision occurs in the DRP reservation and a negotiation reservation having a high priority occupies the MAS 121. The reservation includes set of the MASs 121.
The PCA 123 is the same as an Enhanced Distributed Contention Access (EDCA) method of IEEE 302.11e. That is, the PCA 123 is a method for transferring data through competition with different backoffs and contention windows in 4 queues. The DRP 122 and the PCA 123 is a transferring method for preventing collision of a transfer station in a channel environment.
As described above, the WiMedia reserves a propagation time determined when the data to be transferred from the transmitter are generated in order to enable ultra-high speed data transfer among a plurality of communication objects. That is, the WiMedia reserves a specific time for transferring data in order to prevent collision in transferring data.
When the transmitter transfers data, the conventional WiMedia reserves a propagation time based on the DRP of the WiMedia MAC. To be specific, when the conventional WiMedia does not receive an acknowledge (ACK) frame in transferring the data, data are retransferred. When the data are retransferred, an entire data propagation time of the conventional WiMedia is shortage since the DRP period is already reserved. Therefore, the conventional WiMedia prepares for delay caused by retransfer by transferring the rest data based on a next DRP reservation period or setting up an additional reservation period in advance.
Since the propagation time is limited by an environment, the conventional WiMedia regularly reserves an additional propagation time of 30%. When the channel environment is deteriorated, the additional propagation time of 30% is proper to the reservation time. However, when the channel environment is largely shortage, the additional propagation time of 30% may be not enough. Accordingly, since the rest data which are not transferred within the reservation time should wait until a next reservation time in the conventional WiMedia, the entire transfer delay occurs. On the other hand, when the channel environment is good, the additional propagation time of 30% is wasted in the conventional WiMedia.
Therefore, it is required that the conventional WiMedia provides reliability in data transfer by estimating the channel environment in a wireless personal area network and reserving the propagation time of the DRP period.